Even considering the small number of planets in our solar system, Uranus is odd. A new study of its magnetic field indicates that it is even stranger than we thought.
Let's compare it to Earth. Earth spins on it axis, the imaginary line going through its north and south poles. Earth's axis is not perpendicular to the sun, but tilts about 23 degrees.
This tilt is the reason we have repeating seasons. When Earth is canted so that the Northern Hemisphere is tilted more directly to the sun, we have summer in the north. When it is tilted away from the sun, it is northern winter.
But Uranus is titled 98 degrees to the sun. The sun shines not most directly on its equator like Earth but at one pole -- the only planet so tilted. As the planet orbits the sun, one pole gets 42 days of total sunlight, followed by 42 days of total darkness. Despite this, the area around Uranus's equator is hotter than the poles -- and astrophysicists have no idea why.
We didn't know much about Uranus until NASA's Voyager 2 flew by in 1986. The probe came within 50,000 miles of the planet, sending back data and pictures that showed a smooth blue ball. Its upper atmosphere is now known to be a thick envelope of hydrogen and helium. Below that is an ocean of water and ammonia ice.
Voyager 2 also sent back a lot of data on the planet's magnetic field, including it long, flowing magnetotail that streams away from the planet.
Thirty years later we are still using that that data, but analysis by a team from the Georgia Institute of Technology shows the magnetic field is dramatically skewed. Unlike Earth's magnetic field, which emerges from one pole and enters another, Uranus's magnetic pole is not a pole-pole orientation.
For reasons unknown, the magnetic lines emerge 59 degrees away from one pole.
If Earth were so constructed, a compass needle would point to Jerusalem.
The result? The sort of consistent shielding Earth gets from the brutal solar wind is totally absent above Uranus. As the planet rotates, the magnetic field is always changing orientation. Earth is protected from the solar wind in somewhat consistent ways, but on Uranus sometimes the solar wind is deflected and sometimes It just strikes the planet directly.
As the Uranus day goes on, sometimes the surface receives no violent attack from solar wind, and at other times solar wind strikes the planet directly--all because of the skewed magnetic field.
NASA is now considering expeditions to the planets. If approved, the probes would lift off in 2030 and either fly by or orbit the ice giant.
Don't be surprised if we find Uranus even weirder than we know.
